This is a continuing long-term project in which a large number of non-diabetic relatives of diabetic patients as well as asymtomatic mildly diabetic patients are being studied periodically. In addition to detecting early defects in carbohydrate metabolism, we are seeking to find parameters, other than those associated with carbohydrate metabolism, which will indicate the existence of the prediabetic state. Methods by which the evolution from prediabetes to subclinical diabetes, from subclinical diabetes to latent chemical diabetes, and from latent asymptomatic diabetes to overt diabetes can be modified, are being sought. Young patients with latent (asymptomatic or chemical) diabetes have been studied prospectively for periods of up to 20 years and will continue to be studied to ascertain possible changesin (1) carbohydrate metabolism, (2) insulin secretion, (3) glucagon secretion, (4) growth hormone secretion and (5) the possible evolution of microangiopathy, macroangiopathy and neuropathy.